Rock Damage Model Under Triaxial Condition Based On Energy Dissipation Principle

Rock constitutive model is one of the key points in rock mechanics.At present,scholars at home and abroad have done a lot of experimental research on the constitutive model of rock.Based on the plasticity theory,damage mechanics theory and thermodynamics theory,a large number of rock constitutive models have been proposed.However,with the increase of mining depth,rock dynamic disasters often occur.The existing rock constitutive model can not accurately determine whether the surrounding rock will be transformed from static to dynamic,which brings a huge challenge to the safety production of the mine.In view of the shortcomings of the existing rock constitutive model,this thesis used RLJW-2000 electro-hydraulic servo press to carry out conventional triaxial experiment,and analyzed the deformation and failure characteristics,damage evolution rule and damage dissipation energy of rock.Based on the law of thermodynamics,the damage evolution equation was derived.According to the experimental results,the plastic strain model and the damage energy dissipation model were established.According to the theory of damage mechanics,the damage constitutive model was given.Based on the analysis of the relationship between the release of elastic strain energy and the rate of damage energy dissipation,the criterion of rock transformation from static state to dynamic state was added.In order to make up for the deficiency of the damage constitutive model in describing the nonlinear deformation process of rock in the compaction stage,based on the contact theory,the contact element model was established to describe the nonlinear deformation characteristics of rock.In addition,through the analysis of the macroscopic nonlinear deformation characteristics of the rock in the compaction stage,it is determined that the volume stress is the influencing factor of the nonlinear deformation characteristics in the compaction stage,and the theoretical model of the volume stress causation was established to describe the nonlinear deformation characteristics of the rock.After comparing the applicability of the two models,combined with the damage constitutive model,the damage constitutive model considering the compaction stage was established.By comparing with the experimental results,the rationality and effectiveness of the proposed model were verified.In order to explore the feasibility of this model in engineering practice,based on the explicit Euler algorithm,a finite volume numerical calculation software was developed.The constitutive model proposed in this thesis was further deduced and embedded in the numerical calculation to carry out numerical simulation of the surrounding rock of the field mining face,and to explore the feasibility of the model for stress field calculation,rock displacement calculation and dynamic disaster prediction.Based on the above work the following conclusions are drawn:(1)From the view of fracture surface morphology,when the rock is in the state of low confining pressure,the fracture surface is relatively rough,which is mainly composed of longitudinal splitting and shear failure.With the increase of confining pressure,the fracture surface is gradually flat,and the failure mode is transformed into complete shear failure.The angle between the fracture surface and the radial direction is in the range of 60°?70°.(2)From the relationship between the elastic strain energy and the damage dissipation energy,in the compaction stage and the linear elastic stage,the energy input from the outside to the rock is almost completely stored in the form of the elastic strain energy,and the damage dissipation energy accounts for a small proportion.As the rock enters the plastic yield stage,the proportion of elastic strain energy to total energy decreases gradually,and the proportion of damage dissipation energy increases gradually.When the rock enters the plastic softening stage,the elastic strain energy in the rock releases rapidly,while the dissipation energy increases rapidly.When the rock enters the residual stress stage,the elastic strain energy in the rock is basically unchanged.(3)Compared with the experimental results,it is shown that the damage constitutive model proposed in this thesis can reflect the phenomenon of pre peak strengthening and post peak softening.At the same time,the model reflects that with the increase of confining pressure,the strength of rock can be improved and the rock gradually transforms from brittleness to ductility.The model can accurately describe the stress-strain relationship of rock,which proves the rationality of the model.(4)Through the simulation of rock burst experiment in the process of grading loading,the numerical simulation results show that the "criterion" proposed in this thesis is consistent with the experimental results in predicting the location and timing of rock burst,which proves that the criterion has certain rationality.(5)Using the developed finite volume numerical calculation software to simulate the stress concentration phenomenon of the orifice,the calculation results are compared with the theoretical solutions.The comparison results show that the finite volume numerical calculation software developed in this thesis has high accuracy,which proves the rationality of the software.(6)By using the rock damage constitutive model proposed in this thesis,the numerical calculation of a mining face was carried out.The calculation results show that the model can reflect the distribution law of stress field and displacement field of surrounding rock,which proves that the model in this thesis is reasonable and feasible in the actual engineering calculation process.